Line synchronized strobe light

ABSTRACT

A line synchronized strobe light including an adjustable voltage divider connected across an A. C. source to a diode at the division point thereof where the diode periodically charges up a capacitor. The capacitor is connected to discharge through a neon which is placed in electrostatic proximity with the input lead bearing the same polarity as the diode. When the neon reaches a triggering level it both discharges the capacitor and triggers an SCR connected to complete a circuit across a strobe light. The strobe light bulb is filled with a mixture of Helium and Argon in order to give both a fast turn off time and to limit the evaporation of the filament thereof.

United States Patent [1 1 Liebman 1 1 Oct. 29, 1974 LINE SYNCHRONIZED STROBE LIGHT Theodore Liebman, 8201 Henry Ave, Philadelphia, Pa. 19128 [76] Inventor:

Primary Examiner-Herman Karl Saalbach Assistant Examiner.lames B. Mullins Attorney, Agent, or FirmFulwider, Patton, Rieber, Lee & Utecht [57] ABSTRACT A line synchronized strobe light including an adjustable voltage divider connected across an A. C. source to a diode at the division point thereof where the diode periodically charges up a capacitor. The capacitor is connected to discharge through a neon which is placed in electrostatic proximity with the input lead bearing the same polarity as the diode. When the neon reaches a triggering level it both discharges the capacitor and triggers an SCR connected to complete a circuit across a strobe light. The strobe light bulb is filled with a mixture of Helium and Argon in order to give both a fast turn off time and to limit the evaporation of the filament thereof.

7 Claims, 3 Drawing Figures PAIENIEU 06F 29 am FIG.3

LINE SYNCHRONIZED STROKE LIGHT BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to variable frequency pulse generators, and more particularly to pulse generators synchronized to line frequency for powering strobe lights of a fractional frequency thereof.

2. Description of the Prior Art In many applications, particularly in an entertainment industry, various lighting devices are operated at a frequency to provide visual effects. One of such effects was to provide strobe or flashing lights of high intensity usually set to cycle at a frequency below the optical cutoff of a human eye, to enhance or modify theatrical staging and the like. In these applications, it has been the usual object to provide a disorienting effect to the stage scene by flashes of high intensity and short duration flashed at repeatable intervals. Furthermore, in order to accommodate the various desired effects of this kind, it has been a further requirement that the frequency of the flashes be adjustable to provide flexibility in developing any particular effects.

Heretofore, such devices have been complex, requiring D. C. power supplies to operate the timing circuit and to power the light source, including extensive synchronization circuitry to provide line synchronization. Furthermore, the components of the various prior art circuits had to be of a select high accuracy group, adding cost and complexity to the circuit. Such complex circuitry usually increases failure rates and often requires high standards of competence in calibration and adjustment.

SUMMARY OF THE INVENTION Accordingly, it is the general purpose and object of the present invention to provide a power pulse circuit capable of driving high intensity light devices over extended pulsing sequences at any frequency division of a conventional A. C. source.

Other objects of the invention are to provide a pulse circuit directly coupled to an A. C. line which is simple and reliable, requiring a minimum of precision parts and which consistently produces pulse widths substantially equal to one half cycle of the source.

These and other objects are accomplished in the present invention by connecting a resistive voltage divider connected in shunt across a conventional power source, such as a home current outlet, where either one or both of the legs of the voltage divider are adjustable to any desired level of division. The center lead of the voltage divider is connected to yet another variable resistor which, at the other end thereof, connects across a diode to one end of the capacitor and to a neon. The output terminal of the neon is connected to the gate terminal of the silicon controlled rectifier. The rectifier completes the circuit, between a load on one lead from the source, such as a helium-argon incandescent lamp, and the other end from the source. In this manner, whenever the SCR is triggered to conduct, the lamp is energized producing a flash. The neon is further physically located in close proximity with the electrostatic field of the A. C. positive lead utilizing electrostatic and capacitive effects across the glass thereof to generate a small current on the inside which reduces its triggering voltage. In particular the effect of a charge of the same polarity as the anode of the neon is to generate ions on the inside thereof in parallel with the anode to cathode path, thereby decreasing the required voltage to drive the neon into a conductive avalanche. Thus, an increasing electrostatic field is capacitively coupled with the inside of the neon across the glass walls thereof, where the glass forms the dielectric separation of a capacitor, producing a small current to the triggering voltage of the neon. Such decrease in triggering voltage has a maximum immediately after the positive zero crossing of the A. C. signal, assuring pulse initiation substantially concurrent with the zero crossing. After the neon is initiated or triggered, it will continue to conduct, discharging the capacitor to a voltage level below the maintaining voltage thereof. In this manner, the neon provides a gating signal to the rectifier essentially proximate the positive going zero crossing of the A. C. signal, assuring that the SCR conducts for substantially one half of the cycle of the A. C. source. The light source is an incandescent bulb including a glass container enclosing a mixture of Helium and Argon where the Argon, due to its relatively high molecular weight, decreases the evaporation rate of the filament.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schemmatic of a circuit illustrating the preferred embodiment constructed according to the invention;

FIG. 2 is a top view of a printed circuit board illustrating the mechanical arrangement of the circuit elements of FIG. 1; and

FIG. 3 is a time sequence diagram illustrating signal sequences at selected points of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, a conventional source of electrical power E, such as a home power outlet, is connected to a connector 1] on a printed circuit assembly 10. On the other side of connector 11, the two leads are shunted by a voltage divider 12, comprising an upper variable resistor or potentiometer I5 connected in series with a lower potentiometer 16. The common junction between potentiometers 15 and 16 forms a division pick-off D which is connected to one end of the variable center resistor I7. At the other end, resistor 17 is connected across a diode 22, oriented to pass positive voltages only, to the input terminal of a neon 20 and to one end of a capacitor 21. At the other end, capacitor 21 connects to the negative lead from connector 11, whereby capacitor 21 continues to increase in charge, during each conductive cycle of diode 22 until neon switch 20 is triggered. The other end of switch 20 connects across a ballast resistor 23 to the gate terminal of a silicon controlled rectifier 24 and across an R. C. circuit 25 to the negative lead from connector II. Rectifier 24 completes a circuit between a load L which is connected in series with a positive temperature coefficient resistor 27 and the negative lead. At the other end, load L connects to the positive lead, such that as the SCR 24 is gated to conduct the load L is energized.

As shown in FIG. 2, the positive terminal of plug 11 extends to form a conductor 31 arranged along one edge of a printed circuit board 30, where the negative terminal extends in the form of a conductor 32 arranged proximate the opposite edge of the printed circuit board. Voltage divider 12 is connected across conductors 31 and 32, connecting at junction D across a resistor 17 to a diode 22. At the output end, diode 22 connects to a conductor 35 which is also connected to one end of capacitor 21 and the input terminal of the neon 20. (Conductor 31 is extended to form a conductor 38 disposed to surround neon and having a strap 36 connected thereacross.) In this manner, neon 20 is exposed to the electrostatic field of the A. C. lead to the circuit. The changes in the electrostatic field induce a capacitive effect across the glass of the neon, producing on the inside thereof small currents to cathode in parallel with the anode to cathode current. When the electrostatic field is increasing, the capacitive current is in addition to the anode to cathode current and thereby reducing triggering voltage of neon. When the electrostatic field is decreasing, the capacitive current is in subtraction to anode to cathode current and the trigger voltage is increased. It should be noted that the largest change in the electrostatic field, and concurrently the largest amount of current passed across the capacitor formed by the glass thereof, occurs proximate the zero crossings of the A. C. signal. Thus, a differential effect takes place cross the neon glass, providing a lower triggering voltage of the neon immediately after the positive zero crossing of the A. C. signal.

The operation of the present invention will now be set forth with particular reference to FIG. 3. The volt age potential between the two terminals of connector H is shown as an alternating signal A corresponding to the amplitude and frequency of a conventional A. C. source. The voltage at the division point D of the voltage divider is shown as a signal 8 of the same phase and frequency but lower amplitude than signal A, where a signal C corresponds to signal B passed through diode 22. Shown immediately below signals A, B and C is a voltage level V corresponding to the fluctuation in triggering voltage of the neon 20 with variations and electrostatic shield. Typically, a neon will switch into conductive state at about 80 volts, however, in the presence of a strong field, such triggering levels have been observed to decrease to as low as 70 volts. This secondary effect, as previously set out, has strongest manifestations proximate the zero crossing of the A. C. signal. Simultaneously, the capacitor 2 is continually charged by the output of diode 22 until the voltage level of the capacitor shown as signal F, reaches the triggering voltage of the neon at a point where the triggering voltage of the neon is decreased by the electrostatic effect. Thus, by proper selection of the resistors l5, l6 and 17, a charging rate across capacitor 21 can be developed which repeatedly will discharge across the neon when the neon is triggered into a conductive state at the neons lowest triggering level. In this manner, neon triggering can be selectively set by the variable resistors of voltage divider to occur subsequent to a predetermined number of cycles passed by diode 22. Furthermore, since the triggering level of the neon is at its lowest proximate to the positive zero crossing of the A. C. signal, the SCR gated by the neon is gated into a conductive state substantially over the whole positive section of the A. C. cycle. Accordingly, a repeatable width and amplitude signal is produced across the load, a predetermined number of cycles of the A. C. signal apart producing a repeatable high intensity or constant intensity flash to be utilized for various staging effects. The

strobe light or load L compresses an incandescent light having a filament disposed in a mixture of Helium and Argon, substantially mixed at to Helium and I5 to 25% Argon by weight, where the helium, due to its light molecular weight, quickly reduces in temperature allowing quick turn-off times and the Argon inhibits the evaporation rate of the filament, increasing its life. Furthermore, resistor 27 is connected in series with load L, including intimate contact therewith, such that once the load reaches an operating temperature resistor 27 decreases the power thereto.

Some of the many advantages of the present invention should now be readily apparent. The invention utilizes the electrostatic effects of the neon to best advantage to provide a convenient manner of switching a silicon rectifier and thereby driving a load. Furthermore, in this configuration, the charging rate of the capacitor can be selected to positively intercept the neon minimum triggering level after a predetermined number of charging cycles.

Obviously, many modifications and variations of the present invention may be made with regard to the foregoing detailed description without departing from the spirit of the invention.

1 claim:

1. Apparatus for producing light flashes at a predetermined frequency, comprising:

voltage dropping means adapted to receive an A.C.

signal for producing a reduced A.C. signal at a preselected ratio thereof;

rectifying means connected to receive said reduced A.C. signal for passing signal segments of a predetermined polarity thereof;

capacitive means connected to receive said signal segments for storing an electrical charge corresponding to the accumulated energy of said signal segments;

first switching means connected at one end thereof to said capacitive means and said rectifying means including electrostatic coupling means responsive to said A.C. signal for switching said first switching means into conductive state upon a predetermined combination of the charge on said capacitive means and said A.C. signal;

second switching means connected to be gated to the other end of said first switching means for conducting electrical signals upon being gated by said first switching means; and

lighting means connected in series with said second switching means and in shunt across said A.C. signal for producing light when said second switching means is conducting.

2. Apparatus according to claim 1 wherein said first switching means including a neon lamp connected at one terminal thereof to said rectifying means and connected for gating said second switching means.

3. Apparatus according to claim 2 wherein said volt age dropping means includes a voltage divider adapted to be connected across said A. C. signal and connected at the division point to said rectifying means.

4. Apparatus according to claim 3 wherein said lighting means includes an incandescent light having a filament disposed in a transparent container filled with a predetermined mixture of gases.

5. Apparatus according to claim 4 wherein said mixture of gases consists of a combination of 15 to 25% Argon and 75 to 85% Helium.

lamp is disposed in electrostatic proximity with said positive conductor and said rectifying means including a diode disposed to conduct positive signals from said 5 voltage divider. 

1. Apparatus for producing light flashes at a predetermined frequency, comprising: voltage dropping means adapted to receive an A.C. signal for producing a reduced A.C. signal at a preselected ratio thereof; rectifying means connected to receive said reduced A.C. signal for passing signal segments of a predetermined polarity thereof; capacitive means connected to receive said signal segments for storing an electrical charge corresponding to the accumulated energy of said signal segments; first switching means connected at one end thereof to said capacitive means and said rectifying means including electrostatic coupling means responsive to said A.C. signal for switching said first switching means into conductive state upon a predetermined combination of the charge on said capacitive means and said A.C. signal; second switching means connected to be gated to the other end of said first switching means for conducting electrical signals upon being gated by said first switching means; and lighting means connected in series with said second switching means and in shunt across said A.C. signal for producing light when said second switching means is conducting.
 2. Apparatus according to claim 1 wherein said first switching means including a neon lamp connected at one terminal thereof to said rectifying means and connected for gating said second switching means.
 3. Apparatus according to claim 2 wherein said voltage dropping means includes a voltage divider adapted to be connected across said A. C. signal and connected at the division point to said rectifying means.
 4. Apparatus according to claim 3 wherein said lighting means includes an incandescent light having a filament disposed in a transparent container filled with a predetermined mixture of gases.
 5. Apparatus according to claim 4 wherein said mixture of gases consists of a combination of 15 to 25% Argon and 75 to 85% Helium.
 6. Apparatus according to claim 2 wherein said voltage dropping means comprises a circuit board including a positive and negative conductor adapted to be connected across an A. C. signal and voltage divider means connected in shunt across said conductors.
 7. Apparatus according to claim 6 wherein said neon lamp is disposed in electrostatic proximity with said positive conductor and said rectifying means including a diode disposed to conduct positive signals from said voltage divider. 